Systemd and Swift applications

This article is for those who write server-side Swift applications

All applications on the server must be run under the control of some kind of daemon. You may already be using supervisord or systemd.

This article will show you how to simplify your life with systemdby integrating it directly into your application via an SPM plugin.

First, let's look at how we usually work with systemd and what needs to be done to make it work with our application.

Pure systemd

Settings

You need to find examples of a valid config on the Internet, play with it and save it in the right place /etc/systemd/system.

Most developers give up somewhere around here..

State management

After successful configuration, we need to remember to start the service.

To do this, you need to remember a few simple commands:

systemctl start   myapp.service
          restart myapp.service
          stop    myapp.service

Everything is easy here, but you need to remember the name of the configuration file

Removing a service

systemctl stop myapp.service
systemctl start clean --all

Not too hard to remember, but still…

Viewing logs

This is where most developers get lost because the logs are stored somewhere in the depths /var/logs or anywhere else. This is where it comes to the rescue journalctl.

Real time logs

journalctl -u myapp -f

Last few lines

journalctl -u myapp -n 100 --no-pager

I find it a little difficult to remember all of this, and I often just click “up” on the history in the console in search of the desired command

Plugin

A plugin can make your life a lot easier SwiftSystemd.

It provides an easy way to manage all the above-mentioned processes without any headaches.

You only need to do two steps: add it to the project and run the configuration command.

Adding to a project

Open the file Package.swift your application and add just one line:

.package(url: "https://github.com/MihaelIsaev/SwiftSystemd.git", from:"1.0.0")

Setup command

Go to your Swift application folder and run:

swift run systemd install

At this point, the configuration file will be created and the application will be launched.

It is possible to avoid dialogs in the console by passing the parameters in advance:

swift run systemd install -c release -t App -u mike

Listing of the generated configuration file:

[Unit]
Description="AppName"
After=network.target

[Service]
User={user}
EnvironmentFile=/path/to/AppName/.env
WorkingDirectory=/path/to/AppName
TimeoutStopSec=2

Restart=always

ExecStart=/path/to/AppName/.build/{config}/{target}

[Install]
WantedBy=multi-user.target

That's it! You configured your application correctly, and you didn’t have to google or remember anything. Just two simple steps and it's already working.

Logs

One of the most important tasks is viewing logs.

swift run systemd logs

This way you will get real-time logs of your application from journalctl.

swift run systemd logs --limit 100

This is how you can display the latest 100 lines from application logs.

Easy to remember!

State management

Check service activity:

swift run systemd status

You can manage the state of the service using the following commands:

swift run systemd start    # запускает приложение
                  stop     # останавливает приложение
                  restart  # перезапускает приложение
                  disable  # временно отключает приложение
                  enable   # включает приложение

You can also send kill signal to application:

swift run systemd kill

Removing a service

If you no longer need the service, you can easily remove it completely:

swift run systemd uninstall

Conclusion

Now you can throw away all your notes by systemctl And journalctl .

I will be glad to see your commits to the project.